Based on this link, I think we can rule Dupont out of the running as they do not produce ethylene in IL, nonetheless, I have emailed them and asked for more information. Other major competitors include: BASF, Bayer, Dow Agrosciences, Sygenta, Shell Chemical.
http://www.docstoc.com/docs/46915571/DuPont-Agriculture-and-Nutrition---rossir24-0003


Locations where dupont has locations:http://www2.dupont.com/Our_Company/en_US/worldwide/us_illinois.html


EDIT:
"The world's largest ethylene producers in descending order are:
Equistar Chemicals, ExxonMobil, ChevronPhillips, Shell and Innovene (formerly BP),
Other major producers include
BASF, Fina Petrochemicals, Formosa, Lyondell, Sabic, Sinopec, TotalFinaElf, Westlake Petrochemicals."
http://www.plastemart.com/upload/Literature/Ethylene-supply-and-Polyethylene-market.asp
Innovene is only producing ethylene out of their Texas location, their IL location is focused on Bio-fuels
http://www.ineos.com/con_opo.html

This is the link for ethylene at lyondell and they do sell ethylene, but I have emailed asking for Illinois information as information is routed throught their main office in Texas.
http://www.lyondellbasell.com/Products/ByCategory/basic-chemicals/Petrochemicals/Ethylene/index.htm




Chevron Phillips produces Ethylene in Cedar Bayou, Sweeny and Port Arthur, Texas
(http://www.cpchem.com/bl/olefins/en-us/Pages/Ethylene.aspx)

equistar chemicals has facilities in Illinois but I dont think they sell ethylene there. they do sell it at their iowa location http://www.manta.com/c/mtgzrfl/equistar-chemicals-lp


Exxon Mobile has their largest plant located in Europe (http://www.exxonmobil.com/UK-English/about_what_chemicals_fife.aspx) also located in middle east

Shell locations in US:

Deer Park, Texas, USA
Geismar, Louisiana, USA
Martinez, California, USA
Mobile, Alabama, USA
Norco, Louisiana, USA
Port Arthur, Texas, USA
Puget Sound, Washington, USA

other locations found here:
http://www.shell.com/home/content/chemicals/aboutshell/who_we_are/our_locations/manufacturing_locations/manufacturing_locations_accessible_version/

BASF locations:
http://www2.basf.us/corporate/aboutbasfnaftaindex.html

Formosa is located in delaware, los angelos, texas, and new jersey

Westlake Petrochemical: Only producing ethylene out of their Lake Charles, LA facility
http://www.westlake.com/fw/main/Our-Locations-10.html